Field of the Invention
The invention relates to an electronic printed circuit board, which has a memory module and a contact strip that can be inserted into another electronic unit. The memory module has at least nine identically designed integrated semiconductor memories encapsulated in identically designed rectangular housings. The housings are each individually connected to the printed circuit board. One of the semiconductor memories is connected as an error correction chip on the printed circuit board and the rectangular housing of that memory is arranged on the printed circuit board in a manner such that the longer dimension is oriented perpendicular to the contact strip.
Printed circuit boards of this type are inserted into motherboards of personal computers or network computers and serve as the main memory, for example. In network computers, the printed circuit boards are inserted into compartment-type elements having a small height, for which reason the printed circuit boards themselves should also have only a small height (the dimension perpendicular to the contact strip). Therefore, compared with their width, which is essentially determined by the length of the contact strip, insertable printed circuit boards are not very high so that the compartment-type elements can be made very flat.
The height of a printed circuit board essentially depends on the dimensions of the largest components arranged on the printed circuit board. The largest components that are arranged on a printed circuit board are generally housings for semiconductor chips containing integrated circuits. The connections of the semiconductor chips are connected by the housing to corresponding contacts on the printed circuit board that are significantly larger than the chip connections. The housings themselves are also much larger than the integrated circuits and thus concomitantly determine the minimum height of the printed circuit board. In the case of printed circuit boards which carry memory modules, the largest housings are those for semiconductor memories, for example, for SDRAMS (synchronous dynamic random access memories). The housings therefore have a rectangular form and are always arranged on the printed circuit board vertically, i.e they are oriented with their longer dimension perpendicular to the contact strip.
The reason for this arrangement is that one of the semiconductor memories is used as an error correction chip in order to perform error checking on data that will be stored in the rest of the semiconductor memories or that will be read from the memories. The error correction chip is arranged approximately in the center of the contact strip, is arranged above the contact strip, and is arranged vertically, i.e. with the longer dimension of its housing at right angles to the contact strip, because of prescribed lengths of the conductor tracks which connect the error correction chip to the contact strip.
The rest of the semiconductor memories are arranged on both sides of the error correction chip and also on the front and rear sides of the printed circuit board in the same orientation as the error correction chip, so that all of the identically designed semiconductor memories are lined up along the contact strip in a conventional arrangement. The contact strip has electrical contacts on the front side and also on the rear side of the printed circuit board. Equally, the housing-encapsulated semiconductor memories are present both on the front side and on the rear side of the printed circuit board. Only a single error correction chip is provided and is situated, for example, on the front side of the printed circuit board.
In addition to further semiconductor chips that are encapsulated in smaller housings than the memory chips and that are arranged in proximity to the center of the contact strip, the printed circuit board has further, still smaller components, primarily passive components such as resistors and capacitors. In particular, many resistors are arranged in the outer regions of the contact strip. The resistors require a short connection to corresponding contacts of the contact strip.
By contrast, the housing-encapsulated semiconductor memories arranged in the outer regions of the contact strip are arranged at a somewhat larger distance from the contact strip, since their leads to the contact strip are permitted to be longer than the leads of the passive components to the contact strip.
The distance of all of the semiconductor memories from the contact strip is chosen in a uniform fashion, so that the vertically arranged memory housings concomitantly determine a certain minimum height of the printed circuit board. This is composed of the longer dimension of a memory housing, the height of resistors that are arranged between the housings and the contact strip, the height of the contact strip itself, and possibly a safety clearance between the contact strip and the components on the printed circuit board. This safety clearance serves, in the event of a slightly inclined attitude of the printed circuit board during insertion into motherboards, to protect the nearest components on the printed circuit board from mechanical damage, and is chosen to be as small as possible.
In the case of this conventional arrangement, in which the edges of the memory housings lined up along the contact strip are aligned, there is no more leeway for a further reduction of the circuit board height (the height of the printed circuit board perpendicular to the contact strip).